One of the great challenges of modern biomedical research is observing biologic phenomena in animals and people. An important example of this is our limited ability to monitor the course of bacterial infection. An image-based readout of a bacterial infection would allow differentiation of infection from other etiologies, a tailored duration of antibiotic treatment, and identification of antibiotic resistance suggesting an appropriate class of antibiotic. In addition to the clinical and population implications of improved monitoring of bacterial infections, basic researchers do not have simple tools to measure the immune response to the site of a bacterial infection. Again, imaging is suited to address this problem by facilitating in vivo monitoring over space and time. My work seeks to develop imaging-based chemical and synthetic biology technologies that illuminate bacterial pathogenesis, response to antibiotics, the development of antibiotic resistance, and bacterial interactions with the immune system. I propose complementary approaches to accomplish these goals using immune cells delivered into the blood stream that track bacterial biomarkers ?including bacterial surface markers and bacterial enzymes? and using direct bacterial imaging with positron emission tomography (PET). These new approaches leverage concepts and techniques I have developed including ?cell-cell proximity reporters?, protein destabilizing domains, and PET imaging based on the antibiotic trimethoprim (TMP). Advantages of using immune cells include the ability to generate multiplexed sensors and reporter outputs, transcriptional and enzymatic signal amplification, and regional assessment of immune cell trafficking. An advantage of direct bacterial imaging is the ability to image the bacterial load that does not depend on immune cell access to the infection. The primary objectives of this proposal are 1) to develop new receptors that can report the severity and species of bacterial infection in vivo. 2) to develop new classes of caged small molecules for monitoring immune cell-bacterial cell interactions using synthetic biology principles, and 3) to evaluate a new class of PET radiotracers I recently developed for imaging infection in a rat model of cystic fibrosis (CF) and measure bacterial radiotracer uptake in patients with CF before and after antibiotics. This work builds a foundation to monitor pathologic bacteria in vivo and spans from bench to bedside. I expect to provide sets of reagents to the scientific community including plasmids encoding receptors for a variety of bacteria, enzyme activated small molecules, and useful PET probes, all geared toward specific imaging of live bacteria.